A thin film forming process, which forms a thin film such as a silicon oxide film on target objects (e.g., semiconductor wafers), is performed through a Chemical Vapor Deposition (CVD) method in a manufacture process of a semiconductor device. Such thin film forming process may improve the film quality by reducing an impurity concentration in the film during the film formation at a high temperature. For example, a silicon oxide film (i.e., a High Temperature Oxide (HTO) film) may be formed at a high temperature of about 800 degrees C. by the CVD method.
Further, to greatly improve a resistance against a dilute hydrofluoric acid (DHF) in the silicon oxide film formed by the CVD method, the silicone oxide film is doped with impurity, for example, C2H4, NH3 or the like.
However, doping the silicon oxide film with the impurity such as C2H4 or NH3 may deteriorate resistances against other chemicals (e.g., H3PO4) or affect a device performance. Further, there is a demand for improving the etching resistance against H3PO4 and raising a selectivity ratio against a silicon nitride film.